1. Field of the Invention
The present invention relates to a display device illuminating device, and to a display device. More particularly, the present invention relates to a display device illuminating device, and a display device, that is provided with a plurality of lamps that can be driven in parallel.
2. Description of the Related Art
Common cold cathode lamps used as light sources for display devices have a non-linear negative impedance characteristic, and therefore cannot be driven in parallel. Typically, each cold cathode lamp is provided with a separate power supply circuit. Inconveniently, however, this configuration, requiring as many power supply circuits as there are cold cathode lamps, is costly, and also is disadvantageous in terms of size reduction, weight reduction, and cost reduction.
Moreover, common cold cathode lamps used as light sources for display devices are connected to power supply circuits via harnesses (also called leads) and connectors, and therefore their fitting is troublesome, resulting in poor assembly efficiency with display device illuminating devices employing cold cathode lamps; likewise their removal also is troublesome, resulting in poor replacement efficiency on occasions of replacement of cold cathode lamps, and in poor disassembly efficiency on occasions of discarding of display device illuminating devices employing cold cathode lamps.
Lamps that are free from such inconveniences are external electrode fluorescent lamps (EEFLs) (see, e.g., JP-A-2004-31338 and JP-A-2004-39264), and so are the cold cathode lamps for which the present applicant applied for a patent (see Patent Document 3 listed below).
An external electrode fluorescent lamp is, in terms of an equivalent circuit, a serial circuit composed of a negative resistance and a capacitor connected to each end of it, and thus has a non-linear positive impedance characteristic. External electrode fluorescent lamps can therefore be driven in parallel. On the other hand, a circuit including a cold cathode lamp disclosed in WO 2006/051698 A1, a first power feeding member, and a second power feeding member, the cold cathode lamp being fed with electric power from a power supply device via the first and second power feeding member, is, in terms of an equivalent circuit, a serial circuit composed of a negative resistance and a capacitor connected to at least one end of it, and thus has a non-linear positive impedance characteristic. The cold cathode lamp disclosed in WO 2006/051698 A1 can therefore be driven in parallel.
As discussed above, these lamps can be driven in parallel, with the end portions of the lamps pinched in, under the resilience of holding members made of a resilient metal material (e.g. spring steel). Thus, the lamps can be fed with electric power via the holding members. Conveniently, this construction makes fitting and removal of lamps easy.
The illuminating sections disclosed in WO 2006/051698 A1 will be described. WO 2006/051698 A1 discloses a cold cathode lamp, a first power feeding member, and a second power feeding member, the cold cathode lamp being fed with electric power from a power supply device via the first and second power feeding members, and that is, in terms of an equivalent circuit, a serial circuit composed of a negative resistance, a capacitor connected to one end of the negative resistance, and another capacitor connected to the other end of the negative capacitance.
In a display device illuminating device incorporated in a display device and having a plurality of illuminating sections each of which includes a cold cathode lamp, a first power feeding member, and a second power feeding member, the cold cathode lamp being fed with electric power from a power supply device via the first and second power feeding members, and is, in terms of an equivalent circuit, a serial circuit composed of a negative resistance, a capacitor connected to one end of the negative resistance, and another capacitor connected to the other end of the negative capacitance, adopting a configuration as shown in FIG. 7 in which the equivalent circuits 21 to 24 of those illuminating sections are connected, in parallel with one another, to a power supply device 25 and in which the voltage output from one end of the power supply device 25 and the voltage output from the other end of the power supply device 25 are opposite in phase helps make zero as a whole the power supply noise that enters the display panel via the parasitic capacitance between the display panel and the power supply lines for the illuminating sections.
Inconveniently, however, when attention is focused on one end—call it the first end—of the power supply device 25, all of the illuminating sections receive a voltage of the same phase; thus power supply noise may enter the portion of the display panel corresponding to the first end of the power supply device 15 via a parasitic capacitance, causing display noise. Likewise, when attention is focused on the other end—call it the second end—of the power supply device 25, all of the illuminating sections receive a voltage of the same phase (though opposite to the phase at the first end of the power supply device 25); thus power supply noise may enter the portion of the display panel corresponding to the second end of the power supply device 25 via a parasitic capacitance, causing display noise. In this way, even when the power supply noise that enters the display panel is made zero as a whole, in reality, display noise may appear locally, leading to degraded display quality.